code: def _check_result(assert_result=True):
      """Test the color of each quadrant by picking the center pixel
      of each quadrant and comparing it with the reference color.
      """
      # Take screenshot
      x, y, w, h = gl.glGetParameter(gl.GL_VIEWPORT)
      data = gl.glReadPixels(x, y, w, h, gl.GL_RGB, gl.GL_UNSIGNED_BYTE)
      im = np.frombuffer(data, np.uint8)
      im.shape = h, w, 3
  
      # Get center pixel from each quadrant
      pix1 = tuple(im[int(1 * h / 4), int(1 * w / 4)])
      pix2 = tuple(im[int(3 * h / 4), int(1 * w / 4)])
      pix3 = tuple(im[int(3 * h / 4), int(3 * w / 4)])
      pix4 = tuple(im[int(1 * h / 4), int(3 * w / 4)])
      # print(pix1, pix2, pix3, pix4)
  
      if assert_result:
          # Test their value
          assert_equal(pix1, (0, 0, 0))
          assert_equal(pix2, (255, 0, 0))
          assert_equal(pix3, (0, 255, 0))
          assert_equal(pix4, (0, 0, 255))
  
file_path: vispy/vispy/gloo/gl/tests/test_functionality.py
imports: import sys
  import numpy
  from vispy.app import Canvas
  from vispy.testing import requires_application, requires_pyopengl, SkipTest, run_tests_if_main, assert_equal, assert_true
  from vispy.gloo import gl
  import pytest
label_desc: Use image node_id 12 for calling a global function with example usage: _check_result(assert_result) without return types